Purpose and description

OpenRC is an init system for Unixoid operating systems. It takes care of startup and shutdown of the whole system, including services.
It evolved out of the Gentoo "Baselayout" package which was a custom pure-shell startup solution. (This was both hard to maintain and debug, and not very performant)
Most of the core parts are written in C99 for performance and flexibility reasons, while everything else is posix sh. The License is 2-clause BSD. Current size is about 10k LoC C, and about 4k LoC shell.

Features

OpenRC is known to work on Linux, many BSDs (FreeBSD, OpenBSD, DragonFlyBSD at least) and HURD.

Services are stateful (i.e. start; start will lead to "it's already started")

Startup

rc scans the runlevels (default: /etc/runlevels) and builds a dependency graph, then starts the needed init scripts, either serialized (default) or in parallel.

When all the init scripts are started rc terminates. There is no persistent daemon. (Integration with tools like monit, runit or s6 can be done)

Shutdown

On change to runlevel 0/6 or running "reboot", "halt" etc., rc stops all
services that are started and runs the scripts in the "shutdown" runlevel.

Modifying single services

Any single service can, at any time, be:

started:

# /etc/init.d/someservice start

stopped:

# /etc/init.d/someservice stop

restarted:

# /etc/init.d/someservice restart

OpenRC will take care of dependencies, e.g starting apache will start network
first, and stopping network will stop apache first.

There is a special command zap that makes OpenRC 'forget' that a service is
started; this is mostly useful to reset a crashed service to stopped state
without invoking the (possibly broken) stop function of the init script.

Calling rc without any arguments will try to reset all services so that the
current runlevel is satisfied; if you manually started apache it will be
stopped, and if squid died but is in the default runlevel it'll be restarted.

There is a "service" helper that emulates the syntax seen on e.g. older Redhat
and Ubuntu ("service nginx start" etc.)

Runlevels

OpenRC has a concept of runlevels, similar to what sysvinit historically
offered. A runlevel is basically a collection of services that needs to be
started. Instead of random numbers they are named, and users can create their
own if needed. This allows, for example, to have a default runlevel with
"everything" enabled, and a "powersaving" runlevel where some services are
disabled.

The rc-status helper will print all currently active runlevels and the state
of init scripts in them:

All runlevels are represented as folders in /etc/runlevels/ with symlinks to
the actual init scripts.

Calling rc with an argument ("rc default") will switch to that runlevel; this
will start and stop services as needed.

Managing runlevels is usually done through the "rc-update" helper, but could of
course be done by hand if desired.
e.g. rc-update add nginx default - add nginx to the default runlevel
Note: This will not auto-start nginx! You'd still have to trigger "rc" or run
the initscript by hand.

FIXME: Document stacked runlevels

The default startup uses the runlevels "boot", "sysinit" and "default", in that
order. Shutdown uses the "shutdown" runlevel.

Syntax of init scripts

Init scripts are shell scripts. OpenRC aims at using only the standardized
POSIX sh subset for portability reasons. The default interpreter (build-time
toggle) is /bin/sh, so using for example mksh is not a problem.

OpenRC has been tested with busybox sh, ash, dash, bash, mksh, zsh and possibly
others. Using busybox sh has been difficult as it replaces commands with
builtins that don't offer the expected features.

The interpreter for initscripts is #!/sbin/runscript
Not using this interpreter will break the use of dependencies and is not
supported. (iow: if you insist on using #!/bin/sh you're on your own)

A "depend" function declares the dependencies of this init script. All scripts
must have start/stop/status functions, but defaults are provided. Extra
functions can be added easily:

extra_commands="checkconfig"
checkconfig(){
doSomething
}

This exports the checkconfig function so that "/etc/init.d/someservice
checkconfig" will be available, and it "just" runs this function.

While extra_commands is always available, commands defined in
extra_started_commands will only work when the service is started. This can be
used for implementing graceful reload and similar behaviour.

Adding a restart function will not work, this is a design limitation within
OpenRC. Since there may be dependencies involved (e.g. network -> apache) a
restart function is in general not going to work.
restart is internally mapped to stop() + start() (plus handling dependencies)
(Figuring out a reliable improvement for this "bug" is appreciated)

The depend function

This is a newline-separated list that uses builtins. A little bit 'dirty'
maybe, but simple:

depend(){
need net
use dns logger netmount
}

need

declares a hard dependency - net always needs to be started before this service does

use

is a soft dependency - if dns, logger or netmount is in this runlevel start it before, but we don't care if it's not in this runlevel.

before

declares that we need to be started before another service

after

declares that we need to be started after another service, without creating a dependency (so on calling stop the two are independent)

provide

allows multiple implementation to provide one service type, e.g.: provide cron is set in all cron-daemons, so any one of them started satisfies a cron dependency

keyword

allows platform-specific overrides, e.g. keyword -lxc makes this init script a noop in lxc containers. Useful for things like keymaps, module loading etc. that are either platform-specific or not available in containers/virtualization/...

FIXME: Anything missing in this list?

The default functions

All init scripts are assumed to have the following functions:

start()
stop()
status()

There are default implementations in rc/sh/runscript.sh - this allows very
compact init scripts. These functions can be overriden per init script as
needed.

The default functions assume the following variables to be set in the init
script:

command=
command_args=
pidfile=

Thus the 'smallest' init scripts can be half a dozen lines long

The magic of conf.d

Most init scripts need default values. It would be fragile to explicitly source
some arbitrary files. By convention runscript will source the matching file in
/etc/conf.d/ for any script in /etc/init.d/

So you can set random startup-related things easily. Example:

conf.d/foo:

START_OPTS="--extraparameter sausage"

init.d/foo:

start(){/usr/sbin/foo-daemon ${STARTOPTS}}

The big advantage of this split is that most of the time editing of the init
script can be avoided.

Start-Stop-Daemon

OpenRC has its own modified version of s-s-d, which is historically related and
mostly syntax-compatible to Debian's s-s-d, but has been rewritten from scratch.

It helps with starting daemons, backgrounding, creating PID files and many
other convenience functions related to managing daemons.

/etc/rc.conf

This file manages the default configuration for OpenRC, and it has examples of
per-initscript variables.

Among these are rc_parallel (for parallelized startup), rc_log (logs all boot
messages to a file), and a few others.

ulimit, and CGroups in Linux

Setting ulimit and nice values per service can be done through the rc_ulimit
variable.

OpenRC can optionally use CGroups in the Linux kernel for process management.
By default each init script's processes are migrated to their own CGroup.

By changing certain values in the conf.d file limits can be enforced per
service. It is easy to find orphan processes of a service that persist after
stop(), but by default these will NOT be terminated.
To change this add rc_cgroup_cleanup="yes" in the conf.d files for services
where you desire this functionality.

Caching

For performance reasons OpenRC keeps a cache of pre-parsed initscript metadata
(e.g. depend). The default location for this is /lib/rc/cache/

The cache uses mtime to check for file staleness. Should any initscript change
it'll re-source the relevant files and update the cache

Convenience functions

OpenRC has wrappers for many common output tasks in libeinfo.
This allows to print colour-coded status notices and other things.
To make the output consistent the bundled initscripts all use ebegin/eend to
print nice messages.

Commands

FAQ

How do I tell one startup script to depend on another?

The easiest way to do this is to modify the /etc/conf.d script that corresponds to the service that needs to depend on something else, so let's call this service this_service. Add the following to its conf.d file:

rc_need="other_service"

Now, this_service will depend on other_service.

OpenRC is ignoring dependencies and not reacting to dependency changes

This can happen when your system's time changes suddenly (maybe due to realizing your system clock is wrong and resetting it) and OpenRC dependency cache files are created with future dates. To clear the OpenRC cache, type:

# rc-update -u

Alternatively, you can perform this step manually:

# rm /libexec/rc/cache/*
# rm /libexec/rc/init.d/deptree

Now regenerate the cache by typing:

# /libexec/rc/bin/rc-depend

The OpenRC dependency cache should now be up-to-date and OpenRC should behave properly again.

History

The Gentoo modular init scripts were developed by Daniel Robbins for Gentoo Linux 1.0_rc6 during most of 2001 and released in September 2001 (TODO: add refs). After their development, the dependency-based init script system was maintained by a number of senior developers, starting with Azarah (Martin Schlemmer), with migration to the new init system assisted by Woodchip (Donnie Davies) who converted all ebuild init scripts to work with the new system. As Grant Goodyear notes:

My recollection is that one of woodchip's more impressive early feats was thecomplete replacement of all of the init scripts in Portage for Gentoo Linux1.0_rc6. Through 1.0_rc5 Gentoo had used fairly standard rc scripts modifiedfrom Stampede Linux, but for 1.0_rc6 Daniel Robbins (drobbins) and MartinSchlemmer (azarah) had created a new dependency-based init script system thatis still used today. Within a span of days Donny rewrote every single initscript in the Portage tree and committed new masked packages to await therelease of 1.0_rc6. Thanks to woodchip (and drobbins and azarah, of course) thetransition to the new init scripts was nearly painless. <ref>http://www.gentoo.org/news/en/gwn/20040426-newsletter.xml</ref>

Roy Marples became a Gentoo/Linux developer in 2004 and maintained the modular network scripts for the Gentoo baselayout package. Towards the end of 2005, he became the primary maintainer for baselayout and the init scripts.

At the start of 2007, Roy Marples announced the ongoing development of baselayout-2, containing a rewritten init script coded in C and allowing POSIX sh init scripts instead of forcing the use of bash. By mid 2007, Roy Marples had re-implemented the Gentoo init script design created by Daniel Robbins, using an entirely new code base. Alpha and pre-release baselayout-2 snapshots were added to Gentoo's Portage tree as an optional component.

Towards the end of 2007, Roy Marples retired as a Gentoo developer. Baselayout-2 was still in the pre stage, and aside from the gentoo-fbsd users, it was masked. However, Roy Marples desired to keep the baselayout-2 project moving forward as an independent project. The Gentoo Council permitted Roy Marples to release OpenRC under the 2-clause BSD license, managed by him as an external project.

Around mid-2010, Roy Marples decided to no longer maintain OpenRC. At this point, he transferred development back to Gentoo. However, Daniel Robbins continues to maintain an independent, forked version of OpenRC for Funtoo Linux, which includes a Funtoo-specific network configuration
system.